Single and repeated episodes of endothelial denudation of the aorta will be performed in Wistar rats (normotensive and normolipidemic), in genetically obese rats (hypertensive and hyperlipidenic), and in lean siblings of genetically obese rats (hypertensive and normolipidemic). In each of these animal types the nature history, from insipiency to final status, of the intimal fibrous plaques which form after endothelial removal will be established and the lipid content of aorta will be obtained at various intervals and correlated with the structural damage in the vessel. A major objective is to determine whether the presence of high blood pressure and/or elevated plasma lipids cause progression of the intimal plaques to typical atherosclerosis including such lesions as lipid aggregation, necrosis, hemorrhage and calcific deposit. Antihypertensive drugs and low calorie diet will be employed to control hypertension and hyperlipidemia respectively in order to determine the effect of these regimens on all stages of development of the arterial lesions.